Dual-function hydrogel microspheres coordinate immune regulation and osteogenesis coupling to promote femoral regeneration

The skeletal immune microenvironment plays a critical role in the repair of bone defects; however, current strategies focusing on macrophage M2 polarization and their application in bone regeneration remain limited. To address this, we developed a methacrylated gelatin (GelMA) microsphere system using microfluidic technology, co-loading IL-4 and chitosan-BSA nanoparticles (CNP) encapsulating calcitonin gene-related peptide (CGRP) to achieve temporally controlled release and immuno-osteogenic synergistic regulation. In the early stage, IL-4 secretion promotes macrophage polarization toward the M2 phenotype, improving the inflammatory microenvironment, while the sustained release of CGRP subsequently enhances angiogenesis and osteogenic differentiation, establishing a microenvironment favorable for bone regeneration. In a femoral condyle defect model, these composite microspheres significantly accelerated new bone formation and defect healing, exhibiting an osteogenic pattern centered around the microspheres. This study provides a novel temporally controlled release strategy for promoting bone regeneration through immune microenvironment modulation, offering potential translational value in bone tissue engineering.